Many types of aircraft, including combat airplanes, surveillance aircraft, and unmanned aerial vehicles, utilize panel array antennas. These antennas can be mounted on the outer skin of the aircraft, to radiate and/or receive radio frequency signals. Panel array antennas have a panel architecture, meaning that they are made up of several stacked panels or layers. These antennas may have a top layer that is exposed to the air flowing around the aircraft (the “jet stream”), a radiating layer (including the antenna elements that radiate and/or receive the radio frequency signals), an electronic circuit board layer including the electronics that generate the signal, and a bottom layer for mounting the antenna to the aircraft and connecting the antenna to the power and cooling systems on the aircraft.
Conformal panel array antennas are designed to conform to the exterior shape of the aircraft, so that they do not extend out from the aircraft substantially into the jet stream. Some panel array antennas extend out from the aircraft and into the jet stream flowing around the aircraft, but this design alters the flow of air around the aircraft, increases drag, and requires additional structural modifications and support. A conformal panel array antenna is mounted on or in the aircraft's outer skin, such that the antenna does not extend out into the jet stream. The overall radiation pattern of a conformal array results from the spatial superposition of all of the radiation patterns from the individual antenna elements making up the array.
Many aircraft would benefit from locating these conformal panel array antennas in various places around the aircraft's exterior skin, including the fuselage and wings, and including curved and flat surfaces on the aircraft. However, typical conformal panel array antennas require a cooling system in order to prevent the electronics within the various panel layers from overheating. In the prior art, a cooling plate is mounted on the rear side of the antenna, on the bottom surface of the antenna, opposite the jet stream. This cooling plate includes fluid circulation, fans, and/or heat sinks to draw heat away from the antenna. The cooling plate is powered by the aircraft's on-board power system, and it dissipates heat to the aircraft, such as to the aircraft's environmental control system, or to the aircraft's fuel. Thus, the cooling plate relies on the aircraft for power and cooling.
The need for a cooling element such as the cooling plate on the back surface of the antenna limits the use of conformal array panel antennas, because the cooling plate is typically flat, not curved, and requires operable connections to the aircraft for both power and heat disposal. Accordingly, a conformal panel array antenna with this cooling plate can be mounted on the aircraft skin only at locations where the cooling plate can be both structurally mounted to the aircraft and operably connected to the aircraft's power and cooling systems. Additionally, in drawing power and cooling from the aircraft, the cooling plate reduces the aircraft's available power, resulting in shorter flight duration for the aircraft and/or reduced power for other aircraft systems. The cooling plate also has other disadvantages, such as effectiveness (as it provides cooling only at the back surface of the antenna), weight, space, and cost.
A significant difficulty in designing more effective cooling systems for panel array antennas is the need to prevent leakage of the radio frequency signal that the antenna transmits. In order to prevent the signal from leaking, the antenna typically includes plates or layers that close out the antenna and prevent passage of radio frequency signals, so that the signal can be emitted in the desired direction, rather than radiating out in all directions. However, this closed structure also traps heat inside the antenna and makes cooling difficult. Another problem is the constrained space within the antenna. The electronic devices within the antenna are often packed closely together, limiting the available space for a cooling system.
Accordingly, there is still a need for an improved cooling system for a panel array antenna.